Endoscopes are medical devices which are used to provide external images of organs and structures within a human or animal. As used herein, the term “endoscope” includes, but is not limited to, arthroscopes, colonoscopes, bronchoscopes, hysteroscopes, cystoscopes, sigmoidoscopes, laparoscopes and urethrascopes.
Commonly, endoscopes comprise an insertion portion in the form of a hollow shaft that is designed for insertion through a body orifice or a small incision into an internal body cavity. An objective lens unit consisting of one or more lenses is mounted within the shaft at its distal (forward) end. The objective lens unit forms an image of the area that is viewed by it, i.e., the “target”. The image of the target so captured is then transmitted to an optical viewing device or to an electronic imaging device. The hollow shaft may, but need not, include optical image transmission apparatus, e.g., a relay lens, for applying the image to the optical viewing device or to the electronic imaging device.
A conventional optical endoscope provides an optical viewing capability in the form of an eyepiece unit that is affixed to the proximal (rear) end of the shaft. The eyepiece unit is nominally focused to infinity for direct viewing of the image by the surgeon. More specifically, the objective lens unit of a conventional optical endoscope is usually designed so as to form a focused image of an object or other target located at a predetermined target distance therefrom. That predetermined object distance is the object position relative to the objective lens unit which is thought by the designer to be most frequently required by a surgeon. Further, the overall optics system of a conventional optical endoscope is designed so that the image emerging from the eyepiece unit is collimated, i.e., focused nominally to infinity. The cornea of the surgeon's eye acts to focus the collimated image beam on the retina of the surgeon's eye during direct viewing of the image by the surgeon.
Another type of endoscope is an integrated video endoscope that incorporates a video camera. As used herein, the term “video camera” is used to designate a solid state, electronic imaging device, such as, but not limited to, a charge coupled device (“CCD”) and complementary metal oxide semiconductor (CMOS) imaging devices. In some integrated video endoscopes, the solid state imaging device is mounted within the hollow endoscope shaft, or in a housing that is attached to the proximal end of the shaft. The electronic imaging device generates electrical signals representative of the images received from the objective lens unit. Those signals then are processed to generate video signals which are used to create a video display on a conventional TV monitor or a head-mounted video display unit, for example. In this connection, it should be noted that in addition to the electronic imaging device, the camera may comprise one or more circuits for controlling the operation of the electronic imaging device and processing the electronic imaging device's output signals.
A conventional optical endoscope may be converted to a video endoscope by attaching a video camera to the endoscope in a position to receive the image passed by the eyepiece unit (as used herein the term “video camera” designates a housing that contains a video camera and that is adapted to be connected to an endoscope directly or via an endoscope coupler). The video camera may be used with many different endoscopes, thereby providing significant cost savings over the alternative of providing an integrated video endoscope for each type of surgical procedure. However, since the exit image of the conventional eyepiece unit is generally collimated, and since the target distance will vary as the endoscope is manipulated by the surgeon, it is desirable to provide a focusing device between the video camera and the conventional optical endoscope so that the image passed by the eyepiece unit can be focused so as to accommodate a wide range of object distances. The use of such a focusing device has the effect of changing the magnification, and hence the field of view, of the image, while keeping the image properly focused on the camera image plane.
Known focusing couplers include a focusing lens cell mounted for reciprocal movement within a coupler housing, and a manually movable actuating means located outside of the housing which is mechanically or magnetically coupled to the focusing lens cell for moving the cell so as to focus the image on the image plane of the electronic imaging device of a video camera.
All such externally operable focusing couplers provided for use with conventional optical endoscopes are characterized by several disadvantages. For example, to the extent that such focusing couplers involve externally movable elements having close fitting surfaces, such as manually rotatable focusing rings, the areas between the closely fitting surfaces provide areas into which micro-organisms can enter. These small areas present sterilization issues.
Activation of a focusing system for the lens cell is particularly difficult with steam-sterilizable electronic video endoscopes as the sealed housing precludes direct contact with the focusing system. A known method of focus control includes a rotatable collar that contains permanent magnets that magnetically couple with complementary permanent magnets on the focusing system within the housing. Through magnetic coupling, the user can move the lens cell with respect to the image sensor by rotating the external focusing ring. Since there is no breach of the housing by the magnetic coupling, the hermetic seal is maintained. However, the foregoing system has disadvantages. For example, the magnetic coupling system is bulky, focus precision can be difficult to maintain, and the focusing ring presents sterilization issues.
Steam-sterilizable electronic video endoscopes are known in which an image sensor and lens cell are housed in a hermetically-sealed housing using O-rings, which are adversely affected by repeated heat or steam sterilization. The O-rings fail over time breaching the hermetic seal.
What is needed in the art is a video camera for an endoscope that is hermetically sealed and allows for steam sterilization while incorporating a reliable focusing mechanism.